In uranium enrichment by isotopically selective photoionization of a uranium vapor, such as described in U.S. Pat. Nos. 3,772,519 and 3,939,354 and Pat. application Ser. No. 469,407, filed May 13, 1974, all incorporated herein by reference, there is described apparatus for generating a flowing uranium vapor in which particles of a desired isotope type are selectively ionized.
The rate at which uranium vapor is generated, typically by an electron beam evaporation source, and the distribution of the flow are important system parameters to know and control. Several techniques are available for making this measurement of uranium evaporation rate and include measuring the electron beam current or power input, detecting the accumulation of a deposit from the vapor, detecting the atomic density related to a reference density, and monitoring the emissions of the excited vapor as it passes through the electron beam. These all possess deficiencies in accuracy, reliability or ease of use.
Additionally, in such applications as laser enrichment where further isotopically selective ionization is produced in the vapor flow, it is desired to monitor the operation of this ionization mechanism as well as ion collection effectiveness against a known background ionization in the vapor flow for use in regulation or adjustment of the ionization process.